(A) Field of the Invention
The present invention relates to a shaped article of a liquid crystalline polymer having excellent mold releasability from a die when molding, having excellent thermal and chemical stability without generating decomposition gases etc., having a weld with excellently balanced thermal stability exhibiting a low decrease in strength of a weld, mechanical properties and moldability and having excellent dimensional stability.
(B) Description of the Prior Art
The need for plastic materials having high performance have been growing in recent years. Numerous polymers having various new types of performance have been developed and marketed. However, optical anisotropic liquid crystalline polymers characterized by the parallel sequences of molecular chains, have particularly noted due to their superior flowability, thermal resistance, mechanical properties, and mechanical stability. Examples of such polymers capable of forming an anisotropic melt include, for example, a liquid crystal polyester obtained by copolymerizing polyethyleneterephthalate with p-hydroxybenzoic acid (Japanese Unexamined Patent Publication No. 49-72393), a liquid crystalline polyester obtained by copolymerizing p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid (Japanese Unexamined Patent Publication No. 54-77691), a liquid crystal polyester obtained by copolymerizing 4,4'-dihydroxybiphenyl, terephthalic acid and isophthalic acid with p-hydroxybenzoic acid (Japanese Examined Patent Publication No. 57-24407), a liquid crystalline polyester amide formed from 6-hydroxy-2-naphthoic acid, p-aminophenol and terephthalic acid (Japanese Unexamined Patent Publication No. 57-172921), and a liquid crystalline polyesteramide formed from p-hydroxybenzoic acid, 4,4'-dihydroxybiphenyl, terephthalic acid, p-aminobenzoic acid and polyethylene terephthalate (Japanese Unexamined Patent Publication No. 64-33123).
However, it is also well known in the art that these liquid crystalline polymers have problems including large mechanical anisotropy and dimensional anisotropy. For solving these problems, various attempts have been made. For example, a method wherein a glass fiber is added to a liquid crystalline polymer (Rubber Digest, Vol. 27, No. 8, pp. 7-14, 1975), a method wherein powder in the form of a plate or flake such as mica, talc or graphite is compounded into a liquid crystalline polymer (Japanese Unexamined Patent Publication No. 63-146959). Thus, the anisotropy is relaxed (or decreased) and simultaneously the mechanical properties, thermal resistance, moldability and dimensional stability are further improved. As a result, the liquid crystalline polymer compositions are used, as an engineering plastic, in a wide variety of application fields, such as automobile parts, electrical and electronic parts, precise mechanical parts, office machine parts.
Since liquid crystalline polymers are generally excellent in the flowability thereof, the molding and processing are easy and the liquid crystalline polymers can be used as thin-walled molded products or molded articles having complicated shapes. However, various problems have been pointed out in the molding of such thin-walled molded products and molded articles having complicated shapes such that the dimensional stability thereof becomes poor due to poor mold releasability, the operation to remove the molded articles from the mold, and the productivity is decreased.
Generally, as a method for improving the mold releasability, methods for adding various releasing agents such as fatty acid esters, metal salts of fatty acids, fatty acid amides, low molecular weight polyethylene polymers are added to the liquid crystalline polymers are known in the art. In addition, Japanese Unexamined Patent Publication No. 2-208035 discloses a method for formulating fatty acid esters to liquid crystalline polyesters and Japanese Unexamined Patent Publication No. 4-120162 discloses a method for adding fatty acid esters composed of polyols (e.g., glycerol and pentaerythritol) and fatty acids having 12 or more carbon atoms.
However, when these methods are applied to liquid crystalline polymers, there cause other problems, due to the high processing temperature of the liquid crystalline polymers, that the releasing agents decomposes to generate volatile gases, and therefore, not only the outside appearance of the molded articles is adversely affected, but also the effects of the releasing agents are impaired, whereby the release of the molded article from the die becomes poor and the shape of the molded article is changed (or deformed). Especially, in the case of molded articles having a weld (i.e., which is provided by plural melted resin flows encountering in the mold), the strength at the weld is largely decreased and the strength of the molded articles become poor and the molded articles cannot be practically used due to the shortage in the strength of the molded articles, especially in the weld thereof.